Abstract: A process for sealing the NO compressor and the residual gas expander in a plant for the production of nitric acid by the dual-pressure process uses a low-pressure section, a NO compressor, a high-pressure section with oxidation and absorption, at least one heat exchanger, a residual gas expander, in which ammonia and compressed air are passed into the low-pressure section of the nitric acid plant, where ammonia is oxidised via a catalyst to yield NO and water. The obtained NO is partly oxidised to yield NO2. The NO- and NO2-saturated gas is passed into the NO compressor, the compressed NO- and NO2-saturated gas is passed into the high-pressure section of the nitric acid plant where the residual NO is oxidised to yield NO2, followed by absorption of nitrogen dioxide to nitric acid. The residual gas from the high-pressure section is routed to the residual gas expander via at least one heat exchanger.